The present invention is directed to a drive device for an apparatus for electrical function testing of wiring matrices, particularly of printed circuit boards, having a carrier plate located over the wiring matrices and having a plurality of gas discharge channels each provided with at least first and second electrodes. At least two selected measuring locations (test points) of a wiring matrix are contactable via the allocated gas channels and their electrodes, respectively, whereby every channel being equipped with at least two electrodes is selectable based on a coincidence principle via a plurality of first and second electrode bus lines allocated to these electrodes. First electrodes of the channels are connected to one another in series via the first electrode bus lines and second electrodes of the channels are connected in series to one another via the second electrode bus lines.
European patent document EP-A-O 102 565 discloses a means for electrical function testing of wiring matrices wherein previously standard ohmic contacting of the measuring locations is replaced by non-touching plasma contacting via gas discharge paths. To this end, a plurality of gas discharge channels provided with electrodes are positioned in a carrier plate that can be placed on the wiring matrices. The gas discharge channels arranged in the framework of the wiring matrices are open toward the measuring locations. When, for example, two selected measuring locations are then connected to one another by an electrically conductive interconnect, then the allocated gas discharge channels form two series-connected gas discharge paths that can be ignited by applying an adequately high voltage to the electrodes. A current flow then occurs with the ignition of the gas discharges, this current flow being capable of being interpreted for testing purposes. When the ignition of the gas discharge fails to occur or when an excessively low current flows after an ignition, then it can be concluded that there is an interrupted connection between the selected measuring locations or a connection therebetween did not originally exist. The prior art apparatus thus provides conductivity and insulation measurements, whereby an extremely high reliability is achieved by avoiding ohmic contacts.
In automatic testing units and PC board adapters for unequipped and equipped printed circuit boards as well as for wiring matrices using solder or crimp technology the plurality of measuring locations can amount, for example, to a hundred thousand. Both in the use of resilient test probes as well as ionic contacting via gas discharge paths, the plurality of required leads and switch elements increases with the plurality of measuring locations, whereby a considerable complexity of apparatus and correspondingly high costs result. In order to reduce the plurality of terminals, a prior art arrangement has every gas discharge channel equipped with at least two non-insulated electrodes, whereby one electrode assumes the function of a grating (European patent document EP-A-0 218 058). Only the selection of both electrodes effects an ignition and/or burning of the gas discharges to the printed circuit board, in contrast the ignition and/or burning of a gas discharge from one electrode to the interconnect can be prevented by the other electrode, that is, the grating electrode. When the first electrodes of the gas discharge channels are connected in series via first electrode bus lines and the second electrodes, the grating electrodes, are connected to one another via second bus lines, then the two families of bus lines can be advantageously positioned at a relative angle of 45.degree. .
In this prior art arrangement, a voltage that is adequate to ignite two series-connected discharges is applied between the upper electrode bus lines that are associated with the two test points. In addition, voltages are applied to the lower electrode bus lines that provide an ignition of the upper bus lines connected to a voltage at test points only at the desired measuring points and prevent all other ignitions, whereby no discharge can occur between the two electrodes of one channel.